1. Field of the Invention
This invention relates to a synchronizer for a gear type transmission, and more particularly to a double-cone type synchronizer.
2. Description of the Prior Art
There has been known a gear type transmission for a vehicle in which pairs of gears are provided between an input shaft connected to the engine by way of a clutch and an output shaft connected to the driving wheels and the gear speed is changed by selectively bringing one of the pairs of gears into driving engagement. In the transmission of this type, the gears on one of the shafts are fixedly mounted on the shaft and the gears on the other shaft are mounted so as to be rotatable relative to the shaft with the gears on each shaft always being in mesh with the corresponding gears on the other shaft, and by selectively connecting one of the gears that is rotatable relative to the shaft to a clutch hub fixed to the shaft by way of a hub sleeve, the shafts are operatively connected to each other to transmit the driving force. That is, the rotatably-mounted gears are provided with splines, and the hub sleeve is in engagement with the clutch hub by way of splines to be rotated together with the clutch hub and is axially movable on the outer surface of the clutch hub to be selectively engaged with the splines on one of the rotatably-mounted gears, thereby bringing the rotatably-mounted gear and the clutch hub into driving engagement.
In the gear type transmission having the arrangement described above, a synchronizer is provided to facilitate meshing of the gear spline and the hub sleeve. As the synchronizer, there has been in wide use of a type comprising a cone integrally formed with the rotatably-mounted gear, a synchronizer ring having a tapered surface opposed to the cone and adapted to be engaged with the hub sleeve by way of splines, and a synchronizer key to be moved in response to the sliding motion of the hub sleeve. In the synchronizer, when the hub sleeve is axially slid into engagement with the splines on the rotatably-mounted gear, the synchronizer ring is pushed by the synchronizer key to be frictionally engaged with the cone, thereby bringing the gear spline and the hub sleeve into synchronization prior to meshing thereof. See Japanese Unexamined Utility Model Publication No. 58(1983)-132229, for instance. In a gear type transmission for a truck, especially in the first and second speed gears, the synchronizer ring or the cone is rotated with a large torque and accordingly it is preferred that the clutch capacity or the synchronization capacity between the synchronizer ring and the cone be as large as possible.
Accordingly, there has been proposed a double-cone type synchronizer in which frictional engagements are produced at a pair of parts in order to increase the synchronization capacity. As shown in FIG. 3, the double cone type synchronizer comprises an inner cone 53 having a tapered outer surface and fitted on a shaft 51 (the input shaft or the output shaft), on which a gear 50 is rotatably mounted, to be rotated together with a clutch hub 52, an outer cone 55 having a tapered inner surface opposed to the outer surface of the inner cone 53 and mounted coaxially with a hub sleeve 54, a double cone 57 provided between the inner surface of the outer cone 55 and the inner surface of the inner cone 53 to be rotatable together with the gear 50 and to be axially movable, and a synchronizer key 58 adapted to be moved in the direction of the axis of the hub in response to sliding of the hub sleeve 54 to push the outer cone 55 in the same direction to bring the outer cone 55 into frictional engagement with the double cone 57 and bring the double cone 57 into frictional engagement with the inner cone 53. In the double cone type synchronizer, the inner cone 53 and the outer cone 55 engaged with the hub sleeve 54 by way of splines are brought into frictional engagement with the double cone 57 on opposite sides of the double cone 57 before the hub sleeve 54 is brought into engagement with the gear spline 56, whereby the gear spline 56 and the hub sleeve 54 are brought into synchronization. That is, the synchronization capacity is increased by connecting the gear spline 56 and the hub sleeve 54 rotating at different speeds by way of a pair of frictional engagements.
In the double cone type synchronizer, the inner cone 53 must be rotatable relative to the clutch hub 52 in order to accommodate the difference in the angular position between them at the beginning of the frictional engagement thereof. Accordingly, conventionally, as shown in FIG. 4 the splines 51a on the shaft 51 are formed at relatively large intervals and the spline grooves 53a on the inner cone 53 to be engaged with the splines 51a are formed to have a width larger than the width of the spline 51a. However, this arrangement is disadvantageous in that the number of the splines 51a on the shaft 51 is inherently reduced and the strength of the connection between the shaft 51 and the clutch hub 52 is weakened. Further, when the transmission is required to be compact, the splines on the clutch hub 52 must be shortened in order to mount the inner cone on the shaft 51, which also weakens the strength of the connection.